we know that
volume of a cylinder (tube)=pi*r²*h
in this problem
r=4 cm
Volume of a cylinder (tube)=pi*4²*h------> V=16*pi*h cm³-----> equation 1
density=mass/volume------> solve for volume
volume=mass/density
mass=2,100 gr
density=1.41 gr/cm³
so
V=2,100/1.41--------> V=1,489.36 cm³-------> equation 2
equate equation 1 and equation 2
16*pi*h=1,489.36------- h=1,489.36/(16*pi)-------> h=29.63 cm
therefore
the answer is
the high of the tube will be 29.63 cm